Meiosis is not like another: Gabriela Cabral and Peter Schlögelhofer at the Max F. Perutz Laboratories (MFPL) of the University of Vienna and the Medical University of Vienna dived into the process of meiosis ...

An international team of researchers from Japan and the UK has discovered how a single protein, called PP4, oversees the processing of DNA during sperm and egg generation for successful fertilization. This ...

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From a biological point of view, the world's most exotic sex lives may be the ones lived by fungi. As a kingdom, they are full of surprises, and a new one reported in the journal Nature seems sure to tit ...

Researchers from Heidelberg have decoded a previously unknown molecular mechanism in the fertilisation process of vertebrates. The team of scientists at the Center for Molecular Biology of Heidelberg University identified ...

Neil Hunter's laboratory in the UC Davis College of Biological Sciences has placed another piece in the puzzle of how sexual reproduction shuffles genes while making sure sperm and eggs get the right number ...

Researchers at the University of California, Davis have discovered a key tool that helps sperm and eggs develop exactly 23 chromosomes each. The work, which could lead to insights into fertility, spontaneous ...

After more than a century of study, mysteries still remain about the process of meiosis -- a special type of cell division that helps insure genetic diversity in sexually-reproducing organisms. Now, researchers ...

During the development of gametes, such as egg and sperm cells in humans, chromosomes are broken and rearranged at many positions. Using state of the art technology, the research group of Franz Klein, professor for genetics ...

(PhysOrg.com) -- In a study of egg cells using time-lapse microscopy, researchers at the University of California, San Diego School of Medicine and the Ludwig Institute for Cancer Research have discovered an unusual property ...

In a study of egg cells using time-lapse microscopy, researchers at the University of California, San Diego School of Medicine and the Ludwig Institute for Cancer Research have discovered an unusual property of meiosis - ...

Researchers from Cornell University (NY) provide the first analysis of the function of Bloome syndrome protein (BLM) in mammalian meiosis. Bloome syndrome (BS) is a rare genetic disorder characterized by stunted growth, cancer ...

Meiosis

Meiosis (pronounced /maɪˈoʊsɨs/ ( listen)) is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells.

Whilst the process of meiosis bears a number of similarities with the 'life-cycle' cell division process of mitosis, it differs in two important respects:

Meiosis begins with one diploid cell containing two copies of each chromosome—one from the organism's mother and one from its father—and produces four haploid cells containing one copy of each chromosome. Each of the resulting chromosomes in the gamete cells is a unique mixture of maternal and paternal DNA, ensuring that offspring are genetically distinct from either parent. This gives rise to genetic diversity in sexually reproducing populations, which provides the variation of physical and behavioural attributes (phenotypes) upon which natural selection acts, at a population level, leading to adaptation within the population, resulting in evolution.

Prior to the meiosis process the cell's chromosomes are duplicated by a round of DNA replication, creating a maternal and paternal version of each chromosome (homologs) composed of two exact copies, sister chromatids, attached at the centromere region. In the beginning of meiosis the maternal and paternal homologs pair to each other. Then they typically exchange parts by homologous recombination leading to crossovers of DNA between the maternal and paternal versions of the chromosome. Spindle fibers bind to the centromeres of each pair of homologs and arrange the pairs at the spindle equator. Then the fibers pull the recombined homologs to opposite poles of the cell. As the chromosomes move away from the center the cell divides into two daughter cells, each containing a haploid number of chromosomes composed of two chromatids. After the recombined maternal and paternal homologs have separated into the two daughter cells, a second round of cell division occurs. There meiosis ends as the two sister chromatids making up each homolog are separated and move into one of the four resulting gamete cells. Upon fertilization, for example when a sperm enters an egg cell, two gamete cells produced by meiosis fuse. The gamete from the mother and the gamete from the father each contribute one half of the set of chromosomes that make up the new offsping's genome.

Meiosis uses many of the same mechanisms as mitosis, a type of cell division used by eukaryotes like plants and animals to split one cell into two identical daughter cells. In all plants and in many protists meiosis results in the formation of spores: haploid cells that can divide vegetatively without undergoing fertilization. Some eukaryotes, like Bdelloid rotifers, have lost the ability to carry out meiosis and have acquired the ability to reproduce by parthenogenesis. Meiosis does not occur in archaea or bacteria, which reproduce via asexual processes such as binary fission.